Currently, applications of hybrid switches and inrush current free switching apparatuses in electrical control systems for making and breaking control of power capacitors and other loads are popular, which adopts two unidirectional thyristors connected in anti-parallel, and connected with a mechanical switch (such as a magnetic latching relay and electromagnetic-like switches) in parallel. During the making process, the control unit first controls two unidirectional thyristors to conduct at zero-crossing before the mechanical switch is closed, then controls the mechanical switch to close. The hybrid switches have the following disadvantages:
1. Due to existings of short-circuit, breakdown, self-healing situations for the capacitor loads, the generated current is extremely large in the case of no series reactance, the thyristor has a limited overload capacity itself as a semiconductor device, and is easy to break down.
2. The thyristor has a long conduction time, a low power utilization rate, a low cost effectiveness, a poor overload capacity, and is easy to break down.
Due to above reasons, the rated current of the hybrid switches currently can reach only dozens of amperes. Thus, the hybrid switches have a poor reliability performance.